Need to do a board spin since the ADMCF340 is obsolete.
This is being used for motor control and required fixed point DSP.
Is the ADSP-BF504 the closest choice?
Yes, you are right. ADSP-BF50x family processors are good choice for Motor control applications.
Internal 32M bit flash is available on ADSP-BF504F and ADSP-BF506F parts and Internal ADC is available on ADSP-BF506F part.You can find the more information about these processors in the below links.